This invention relates to clutch applications for automatic transmissions.
Ideally, clutches used in automatic transmissions should engage smoothly. Range clutches typically employ a filter spring to lessen the initial impact of the clutch engaging, resulting in a smoother ride. The spring is positioned between the force acting to engage the clutch and the clutch itself to lessen the impact of the force. Ideally, an impact filter spring should have a small stiffness at small deflections and a monotonically increasing stiffness during deflection (i.e., a stiffness that increases at a constant rate over the deflection range) until a fully loaded condition is reached.
Two kinds of washer springs are typically used in automatic transmissions: wave washer springs and Belleville washer springs. Wave washer springs have a waved surface configuration that affects the stiffness of the spring. Belleville washer springs have a cone-shaped portion that is flattened during deflection of the spring. The wave washer has a stiffness that is a constant between 20 percent and 80 percent of its deflection range. The Belleville washer has a stiffness that decreases monotonically with respect to deflection. Accordingly, neither of these types of springs have the desired characteristic of monotonically increasing stiffness over the deflection range of the spring.
A disk spring assembly for smooth clutch application may include a substantially flat ring-shaped disk having opposed faces and a hole formed in the center of the disk such that the disk has an inner peripheral edge and an outer peripheral edge. The disk may have an inner radius at its inner peripheral edge and an outer radius at its outer peripheral edge. Furthermore, the disk may have a substantially uniform thickness between its opposed faces. The disk may be steel. The assembly may also have a movable first angled plate located adjacent to one opposed face. The assembly may further include a second angled plate located adjacent to the other opposed face such that the inner and outer peripheral edges of the disk are deflected in opposite directions relative to each other when the disk moves toward the second plate during engagement of the clutch. The maximum deflection of the disk may be defined by the angled plates.
The first and second angled plates may each have an angled face. The angled face of the first plate may be located adjacent to a face of the disk such that an angle is formed by the first plate and the disk at the inner peripheral edge. The angled face of the second plate may be located adjacent to the opposed face of the disk such that a substantially equivalent angle is formed by the second plate and the disk at the outer peripheral edge. The first plate may be configured such that it first contacts and applies load at the inner peripheral edge of the disk when it moves toward the disk. Furthermore, the second plate may be configured such that it first contacts and applies a reaction load at the outer peripheral edge of the disk when the disk moves toward the second plate by the first plate. The angled face of each plate may have a substantially equivalent inner and outer radius.
The opposed faces of the disk may be in substantially complete contact with respective angled faces of the plates when the clutch is engaged. Additionally, the maximum deflection of the disk may occur when the opposed faces of the disk are in substantially complete contact with the respective angled faces of the plates. The load applied by the first plate may be uniformly distributed across the substantially completely contacted faces of the disk and the plates.
The stiffness of the disk may increase in proportion to the square of the deflection of the disk. Thus, the stiffness of the disk may increase monotonically with the deflection of the disk. The deflection characteristics of initially flat washer springs are discussed in Almen, J. O. and Laszlo, A., xe2x80x9cThe Uniform-Section Disk Spring,xe2x80x9d Trans. ASME, Vol. 58, no. 4, May 1936, pp. 305-314. The stiffness of the disk may be the ratio of the change in force applied to the disk to the change in deflection of the disk. The stiffness of the disk is represented by S and may be determined in accordance with the following formula:       S    =                            K          1                +                  3          ⁢                      K            2                    ⁢                      d            2                    ⁢                      xe2x80x83                    ⁢          wherein          ⁢                      xe2x80x83                    ⁢                      K            1                              =              Nt        3              ,            K      2        =          N      ⁢              t        2              ,      N    =          E                        (                      1            -                          υ              2                                )                ⁢                  Ma          2                      ,      
    ⁢            1      M        =                  (                                            α              +              1                                      α              -              1                                -                      2                          ln              ⁢                              xe2x80x83                            ⁢              α                                      )            ⁢                        π          ⁡                      (                          α                              α                -                1                                      )                          2              ,            and      ⁢              xe2x80x83            ⁢      α        =          a      b        ,
wherein a represents the outer radius of the disk, b represents the inner radius of the disk, E is Young""s modulus, t represents the thickness of the disk, and "ugr" is Poisson""s ratio. See Almen and Laszlo, supra, pp. 309-312, regarding the derivation of this formula.
A spring assembly for enhancing clutch smoothness may include a substantially flat washer having opposing faces, a first ring-shaped plate with an angled face forming an outwardly conical shape located adjacent to one washer face and a second ring shaped plate with an angled face forming an inwardly conical shape located adjacent to the other washer face, wherein the angled faces are cooperatively configured to contact the respective adjacent faces of the washer when the first plate moves in the direction of the washer during engagement of the clutch.
The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.